Acoustic treatment panel comprising cells which each contain a plurality of conduits

ABSTRACT

An acoustic treatment panel in which each cell includes a plurality of conduits which extend from the porous acoustically resistive structure to the reflective layer of the acoustic treatment panel, each conduit including at least one opening set away from the porous acoustically resistive structure and configured to cause the inside and the outside of the conduit to communicate.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority to French patent application FR17 53556, filed on Apr. 25, 2017, the entire disclosure of which isincorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to an acoustic treatment panel comprisingcells which each contain a plurality of conduits.

BACKGROUND

An acoustic treatment panel comprises at least one cellular structurepositioned between a reflective layer and a porous acousticallyresistive layer in contact with an external environment through whichsoundwaves travel. Such a panel works on the Helmholtz resonatorprinciple. Thus, the cellular structure comprises a plurality of cells,each of which forms an approximately fluid-tight cavity, and the porousacoustically resistive layer comprises a plurality of holes configuredto cause the external environment to communicate with one of thecavities. This type of panel is used in an aircraft nacelle to lessennoise originating from an engine.

In order to attenuate low-frequency noises, document U.S. Pat. No.3,887,031 describes an acoustic treatment panel which comprises, withineach cell, a funnel-shaped conduit which has a first end of large crosssection closed off by a portion of the porous acoustically resistivelayer and a second end of reduced cross section closed off by a portionof the reflective layer. The conduit comprises an opening that causesthe inside of the conduit to communicate with the zone delimited ordefined by the cell and the conduit. The large cross section of thefirst end of the conduit is substantially equal to the cross section ofthe cell.

The disclosure herein seeks to improve the performance of acoustictreatment panels of the prior art.

SUMMARY

To this end, one subject of the disclosure herein is an acoustictreatment panel comprising a porous acoustically resistive structure incontact with an external environment in which during operation soundwaves travel, a reflective layer and at least one cellular structurepositioned between the porous acoustically resistive structure and thereflective layer and configured to compartmentalize a zone between theporous acoustically resistive structure and the reflective layer into aplurality of cells. According to the disclosure herein, each cellcontains several conduits each of which has a first end closed off by aportion of the porous acoustically resistive structure, a second endclosed off by a portion of the reflective layer, and at least oneopening set away from the porous acoustically resistive structure andconfigured to cause the inside and the outside of the conduit tocommunicate.

The provision of a plurality of conduits in each cell makes it possibleto improve the acoustic treatment by reinforcing in particular theattenuation of soundwaves at low frequencies and makes it possible toreinforce the compression resistance of the acoustic treatment panel atthe centre of each cell.

According to other features relating to the conduits:

a ratio between a cross section of the cell and a cross section of aconduit is greater than or equal to 10, preferably greater than 20;

each conduit has a cross section less than or equal to 0.04 cm²;

each conduit has a cross section that is constantly between the firstand second ends;

the conduits are rigid;

the cells are delimited or defined by partitions oriented in a firstdirection and in a second direction perpendicular to the first directionand, in each cell, the conduits are positioned along lines parallel tothe first direction and along rows parallel to the second direction;

each conduit has a circular cross section with a diameter of between 0.5and 2 mm.

According to other features relating to the openings:

each conduit comprises a single opening which takes the form of a slotwhich comprises a longest dimension oriented parallel to an axis of theconduit;

the openings of all the conduits of the one same cell are identical andextend from the reflective layer over a length of the order of one thirdof the total length of the conduits.

Another subject of the disclosure herein is an aircraft comprising anacoustic treatment panel according to one of the preceding features.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become apparent from thedescription of the disclosure herein which is about to follow, whichdescription is given by way of purely illustrative example and withreference to the following, example drawings, in which:

FIG. 1 is a side view of an aircraft;

FIG. 2 is a longitudinal section through part of an air intake of anacelle of the aircraft visible in FIG. 1;

FIG. 3 is a section through a cell of an acoustic treatment panelillustrating a first embodiment of the disclosure herein;

FIG. 4 is a cross section of a cell of an acoustic treatment panelillustrating a second embodiment of the disclosure herein from a firstviewpoint;

FIG. 5 is a cross section of the cell visible in FIG. 4 from a secondviewpoint, the reflective layer not being depicted;

FIG. 6 is a perspective view of part of an acoustic treatment panelillustrating another embodiment, the reflective layer not beingdepicted;

FIGS. 7A through 7D are cross sections through a conduit illustratingvarious embodiments of the disclosure herein;

FIG. 8 is a perspective view of a strip provided with a row of conduitsillustrating an embodiment of the disclosure herein;

FIG. 9 is a perspective view of part of an acoustic treatment panelcomprising several strips as visible in FIG. 8;

FIG. 10 is a section through part of the acoustic treatment panelvisible in FIG. 9;

FIG. 11 is a perspective view of part of an acoustic treatment panelillustrating another embodiment from the inside of the panel;

FIG. 12 is a perspective view of the acoustic treatment panel visible inFIG. 11, from the outside of the panel;

FIG. 13 is a section through the acoustic treatment panel visible inFIG. 11;

FIG. 14 is a perspective view of a strip provided with several rows ofconduits illustrating another embodiment of the disclosure herein;

FIG. 15 is a face-on view of an acoustic treatment panel illustratinganother embodiment of the disclosure herein; and

FIG. 16 is a section through the panel for the acoustic treatmentvisible in FIG. 15.

DETAILED DESCRIPTION

As illustrated in FIGS. 1 and 2, an aircraft 10 comprises severalpropulsion assemblies 12 each of which comprises a nacelle 14 configuredto duct a flow of air 16 towards an engine 18. To do that, the nacellecomprises an air intake 20 which, in the direction in which the streamof air 16 flows, has a lip 22 extended inside by an internal duct 24 toduct the air flow 16 towards the engine 18 and towards the outside viaan exterior surface 26.

In order to limit noise nuisance, the interior duct 24 is formed, atleast in part, of at least one acoustic treatment panel 28. In general,the air intake 20 comprises several acoustic treatment panels 20juxtaposed to form the interior duct 24.

In the remainder of the description, a longitudinal direction is adirection parallel to the direction of the air flow 16 or the drive axisreferenced A18. A radial direction is a direction perpendicular to thedrive axis A18. A transverse direction is a direction perpendicular tothe longitudinal and radial directions. A longitudinal plane is a planepassing through the drive axis A18 and a transverse plane is a planeperpendicular to the drive axis A18.

Although described in an application to an air intake, the acoustictreatment panel of the disclosure herein is not in any way restricted tothis area of the aircraft. It may be positioned in other parts of theaircraft 10 or used for other applications.

The acoustic treatment panel 28 comprises a porous acousticallyresistive structure 30 in contact with an external environment in whichthe flow of air 16 and soundwaves travel during operation, a reflectivelayer 32 and at least one cellular structure 34 positioned between theporous acoustically resistive structure 30 and the reflective layer 32.

The reflective layer 32 comprises at least one nonporous sheet made ofmetal or of a composite material.

The cellular structure 34 is configured to compartmentalize the zonebetween the porous acoustically resistive structure 30 and thereflective layer 32 into a plurality of cells 36. Each cell 36 is moreor less fluid-tight and delimited or defined by at least one lateralwall 35 which forms a tube closed off at a first end by a portion of theporous acoustically resistive structure 30 and at a second end by aportion of the reflective layer 32.

Depending on the embodiment, the cells 36 have cross sections (in aplane of section parallel to the reflective layer 32) which are circularas illustrated in FIGS. 4 and 5, square or rectangular as illustrated inFIG. 6, hexagonal or some other shape.

As a rough indicator as to size, each cell 36 has a cross sectional areaof the order of 1 cm² or more.

The cellular structure 34 may be made of metal or of composite material.

According to one feature of the disclosure herein, each cell 36 containsseveral conduits 38 each of which has a first end 38.1 closed off by aportion of the porous acoustically resistive structure 30, a second end38.2 closed off by a portion of the reflective layer 32, and at leastone opening 40 set away from the porous acoustically resistive structure30 and configured to cause the inside and the outside of the conduit 38to communicate with one another.

The ratio between the cross section of the cell 36 and the cross sectionof a conduit 38 is greater than or equal to 10, and preferably greaterthan 20.

Each conduit 38 has a cross sectional area less than or equal to 0.04cm². Each conduit 38 has a cross section that is constant between thefirst and second ends 38.1 and 38.2.

According to one embodiment, the conduits 38 are rigid. They are made ofmetal or of composite material.

According to one embodiment, each conduit 38 comprises a single opening40 which takes the form of a slot the longest dimension of which isoriented parallel to the axis of the conduit 38. Each opening 40 extendsover a portion of the circumference of the conduit 38, which portion isless than or equal to half the circumference.

According to an embodiment visible in FIGS. 4 and 5, the openings 40 ofall the conduits 38 of the one same cell 36 are identical and extendfrom the reflective layer 32 over a length of the order of one third ofthe total length of the conduits 38. Of course, the disclosure herein isnot restricted to this embodiment. As illustrated in FIG. 3, for the onesame cell, the openings 40 may be different and/or positioneddifferently from one conduit 38 to the other. The conduits 38 and theopenings 40 may all be identical within a cell and different from onecell to the other.

According to a configuration visible in FIG. 6, the cells 36 each have asquare or rectangular cross section and are delimited or defined bypartitions 35 oriented in a first direction and in a second directionperpendicular to the first direction. According to one embodiment, thefirst direction is parallel to the longitudinal direction.

Within each cell, the conduits 38 are positioned, in lines parallel tothe first direction and in rows parallel to the second direction.

According to an embodiment illustrated in FIG. 7A, each conduit 38 has acircular cross section with a diameter of between 0.5 and 2 mm.

According to other embodiments illustrated in FIGS. 7B, 7C and 7D, eachconduit 38 respectively has a square or rectangular, hexagonal orelliptical cross section.

Providing several conduits of small cross section within each cell makesit possible to treat sound waves at low frequencies and limits the riskof the acoustic panel becoming crushed in the middle of each cell.

According to another feature, the porous acoustically resistivestructure 30 comprises at least one external layer 42 which is incontact with the airstream 16 and which has through holes 44, internalstrips 46 comprising openings 48 each of which communicates with theinside of a cell 36 via a conduit 38 and connecting canals 50,interposed between the external layer 42 and the internal strips 46,which communicate, on the one hand, with at least one of the throughholes 44 of the external layer 42 and, on the other hand, with at leastone of the openings 48 of one of the internal strips 46. The connectingcanals 50 make it possible to ensure that the small-section openings 48communicate with at least one through hole 44 of the external layer 42.

Depending on the circumstances, the external layer 42 is made of metalor of composite material or comprises a superposition of several layersof metal and/or of composite material.

Depending on the embodiment, the through holes 44 are circular, asillustrated in FIG. 9, and oblong, as illustrated in FIGS. 12 and 15.

According to one embodiment visible in FIG. 8, each internal strip 46comprises a row of conduits 38. According to another embodiment visiblein FIG. 14, each internal strip 46 comprises several rows of conduits38, arranged in a staggered configuration.

For each internal strip 46, the conduits 38 are attached to the internalstrip 46 before it is assembled with other internal strips 46 or otherelements of the acoustic treatment panel.

The internal strips 46 and the conduits 38 may be made of metal or ofcomposite material and are joined together by welding or bonding. As analternative, each internal strip 46 and its conduits 38 are produced byadditive manufacturing.

Each strip 46 comprises two parallel lateral edges 46.1 and 46.2, and amiddle zone 46.3 interposed between the lateral edges 46.1 and 46.2which has the openings 48 communicating with the conduits 38.

According to a first embodiment visible in FIG. 8, one of the lateraledges 46.2 has a swage 51. The internal strips 46 are assembled in afluid-tight manner with one another by superposing the lateral edges46.1 and 46.2 of two adjacent interior strips 46, 46′ to form aninternal layer 52, as illustrated in FIG. 10. Away from the openings 48,the internal layer 52 obtained is fluid-tight, and this contributestowards making the cells 36 fluid-tight.

According to this embodiment, when the internal strips 46 are assembled,the lateral edges 46.1 of the various internal strips 46 form contactsurfaces 46.1F and the middle zones 46.3 of the internal strips 46 areoffset in relation to these contact surfaces 46.1F and each form achannel 46.3F.

Thus, as illustrated in FIG. 10, when the internal layer 52 is assembledwith the external layer 42, the middle zones 46.3 of the internal strips46 are spaced away from the internal layer 42, and each channel 46.3Fclosed by the external layer 42 forms a connecting canal 50.

In order to increase the cross section of the connecting canals 50,foils are interposed between the internal layer 52 and the externallayer 42. Each foil takes the form of a strip of material. These foilslie parallel to one another and are spaced apart. Depending on theconfiguration, the foils are oriented parallel to the lateral edges 46.1and superposed therewith or are oriented at right angles to the lateraledges 46.1.

According to a second exemplary embodiment visible in FIGS. 11 through13, the internal strips 46 are planar and joined together byintermediate strips 54 to form an internal layer 52. The lateral edge46.1 of a first internal strip 46 is superposed on and connected, in afluid-tight manner by any appropriate means, to one of the edges of anintermediate strip 54, and the lateral edge 46.2 of a second internalstrip 46′ is superposed on and connected, in a fluid-tight manner by anyappropriate means, to the other edge of the intermediate strip 54.

Away from the openings 48, the interior layer 52 achieved isfluid-tight, thereby contributing to making the cells 36 fluid-tight.

Each intermediate strip 54 offers a contact surface 54F. Because theintermediate strips 54 are spaced apart, the middle zone 46.3 of eachinternal strip 46 delimits, between two intermediate strips 54, achannel 46.3F.

Thus, as illustrated in FIG. 11, when the internal layer 52 is assembledwith the external layer 42, the middle zones 46.3 of the internal strips46 are spaced away from the internal layer 42 and each channel 46.3Fclosed by the external layer 42 forms a connecting canal 50.

In order to increase the cross section of the connecting canals 50,foils 56 are interposed between the internal strips 46 and the externallayer 42. Each foil 56 takes the form of a strip of material. The foils56 lie parallel to one another and are spaced apart. Depending on theconfiguration, the foils 56 are oriented parallel to the lateral edges46.1 and superposed therewith or are oriented at right angles to thelateral edges 46.1, as illustrated in FIGS. 11 through 13.

According to a third embodiment visible in FIGS. 15 and 16, the externallayer 42 comprises, on its face oriented towards the interior strips 46,mutually parallel and spaced-apart channels 58 into which the throughholes 44 at least partially open. Between each of the channels 58, theexternal layer 42 comprises contact surfaces 42F which form anadditional thickness by comparison with the bottoms of the channels 58.The internal strips 46 are assembled with the internal layer 42 in sucha way as to close each channel 58 to obtain connecting canals 50. Forthis purpose, for each channel 58, the first lateral edge 46.1 of aninternal strip 46 is connected in a fluid-tight manner to a firstcontact surface 42F positioned on a first side of the channel 58, andthe second lateral edge 46.2 of the internal strip 46 is connected in afluid-tight manner to a second contact surface 42F′ positioned on asecond side of the channel 58.

While at least one exemplary embodiment of the invention(s) is disclosedherein, it should be understood that modifications, substitutions andalternatives may be apparent to one of ordinary skill in the art and canbe made without departing from the scope of this disclosure. Thisdisclosure is intended to cover any adaptations or variations of theexemplary embodiment(s). In addition, in this disclosure, the terms“comprise” or “comprising” do not exclude other elements or steps, theterms “a”, “an” or “one” do not exclude a plural number, and the term“or” means either or both. Furthermore, characteristics or steps whichhave been described may also be used in combination with othercharacteristics or steps and in any order unless the disclosure orcontext suggests otherwise. This disclosure hereby incorporates byreference the complete disclosure of any patent or application fromwhich it claims benefit or priority.

The invention claimed is:
 1. An acoustic treatment panel comprising: aporous acoustically resistive structure in contact with an externalenvironment in which during operation sound waves travel; a reflectivelayer and at least one cellular structure positioned between the porousacoustically resistive structure and the reflective layer and configuredto compartmentalize a zone between the porous acoustically resistivestructure and the reflective layer into a plurality of cells; and eachof the plurality of cells containing several conduits, each of which hasa first end closed off by a portion of the porous acoustically resistivestructure, a second end closed off by a portion of the reflective layer,and at least one opening set away from the porous acoustically resistivestructure and configured to cause an inside and an outside of theconduit to communicate.
 2. The acoustic treatment panel according toclaim 1, wherein a ratio between a cross section of the cell and a crosssection of a conduit is greater than or equal to 10, or greater than 20.3. The acoustic treatment panel according to claim 2, wherein eachconduit has a cross section less than or equal to 0.04 cm².
 4. Theacoustic treatment panel according to claim 1, wherein each conduit hasa cross section that is constant between the first and second ends. 5.The acoustic treatment panel according to claim 1, wherein the conduitsare rigid.
 6. The acoustic treatment panel according to claim 1, whereineach conduit comprises a single opening which takes a form of a slotwhich comprises a longest dimension oriented parallel to an axis of theconduit.
 7. The acoustic treatment panel according to claim 6, whereinopenings of all the conduits of one same cell are identical and extendfrom the reflective layer over a length of an order of one third of atotal length of the conduits.
 8. The acoustic treatment panel accordingto claim 1, wherein the cells are defined by partitions oriented in afirst direction and in a second direction perpendicular to the firstdirection and wherein, in each cell, the conduits are positioned alonglines parallel to the first direction and along rows parallel to thesecond direction.
 9. The acoustic treatment panel according to claim 1,wherein each conduit has a circular cross section with a diameter ofbetween 0.5 and 2 mm.
 10. An aircraft comprising an acoustic treatmentpanel, comprising: a porous acoustically resistive structure in contactwith an external environment in which during operation sound wavestravel; a reflective layer and at least one cellular structurepositioned between the porous acoustically resistive structure and thereflective layer and configured to compartmentalize a zone between theporous acoustically resistive structure and the reflective layer into aplurality of cells; and each of the plurality of cells containingseveral conduits, each of which has a first end closed off by a portionof the porous acoustically resistive structure, a second end closed offby a portion of the reflective layer, and at least one opening set awayfrom the porous acoustically resistive structure and configured to causean inside and an outside of the conduit to communicate.